Agricultural soil redistribution and landscape complexity

A number of hypotheses and conceptual models, particularly those emphasizing nonlinear dynamics and self-organization, postulate increases or decreases in complexity in the evolution of drainage basins, topography, soils, ecosystems, and other earth surface systems. Accordingly, it is important to determine under what circumstances and at what scales either trend might occur. This paper is concerned with changes in soil landscape complexity due to redistribution of sediment by fluvial, aeolian, and tillage processes at historical time scales in an agricultural field system near Grifton, North Carolina. Soil mapping and soil stratigraphic investigations were used to identify and map soil changes associated with erosion and deposition by water, wind, and tillage; reconstruct the pre-agricultural soil pattern; and identify transformations between soil types. The Kolmogorov entropy of the pre- and post- agricultural landscapes was then compared. The soil transformations associated with erosion and deposition created four distinct new soils and made possible new transformations among soil series, increasing the number of soil types from seven to 11 and the number of possible transformations from 14 to 22. However, the entropy and complexity of the soil landscape decreased, with associated increases in information and redundancy. The mass redistributions created a lower-entropy landscape by concentrating particular soils and soil transformations in specific landscape settings. This result is contrary to studies showing a trend toward increasing pedological complexity at comparable spatial scales, but over much longer time scales. These results point to the importance of temporal scale, and to the fact that environmental complexity is influenced by factors other than the number of different landscape units present.     

Determination of decisional cut-off values for the optimal diagnosis of bovine tuberculosis with a modified IFNγ assay (Bovigam®) in a low prevalence area in France

The Bovigam(?) gamma interferon (IFNγ) assay was used to complement official skin-test screening in a low bovine tuberculosis (bTB) prevalence region in France. The aim of our work was to determine decisional cut-off values for protein purified derivatives (PPD) and ESAT6-CFP10 antigens (R) in order to optimize the efficacy of the modified Bovigam(?) test, in this low-prevalence area, for optimal classification of infected or non-infected herds following positive skin tests. The sensitivity of the IFNγ assay relative to post-mortem bTB-positive animals (Se(r)) was studied in 60 cattle from 20 bTB-infected herds. Its absolute specificity (Sp) was studied in 492 cattle from 25 bTB-free herds from a bTB-free zone. Its operational specificity (relative to the positive skin test) (Sp(r)) was also studied in 547 skin-test positive cattle from 172 bTB-free herds from an infected zone. Using normalized interpretations for individual (PPD or R) results, the cut-off values at 0.02 for PPD and 0.01 for R were obtained with a view to employ them in low prevalence areas with no previously observed non-specific reactions to SITT. Concerning its use after positive skin tests, cut-off values were set at 0.05 for PPD and at 0.03 for R. The choice of an interpretation method considering positive results with PPD and/or R (PPDUR), justified in a high risk context, provided a test Se(r) of 93% [84-98] and Sp(r) of 71.8% [67.9-75.6]. Analysis of positive results with PPD and R (PPDUR), ideal for low-risk contexts, provided a test Sp(r) of 94.3% [92.0-96.1] and Se(r) of 77% [64-87]. Thus, adapting the criteria to the region's infection status and to the conditions for its application is essential for the appropriate use of the IFNγ assay.